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X-CSE-ConnectionGUID: ErSJxBeTQK2s89D7ysc3JQ== X-CSE-MsgGUID: 8TuBeqMrT6GaWO4rKaNAqA== X-IronPort-AV: E=McAfee;i="6800,10657,11786"; a="79674106" X-IronPort-AV: E=Sophos;i="6.23,236,1770624000"; d="scan'208";a="79674106" Received: from fmviesa009.fm.intel.com ([10.60.135.149]) by orvoesa113.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 14 May 2026 23:46:23 -0700 X-CSE-ConnectionGUID: 234uUvIkTV+YfgBeTmh5FQ== X-CSE-MsgGUID: e/SZAEWjRwmj6Pi0YKa5PA== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.23,236,1770624000"; d="scan'208";a="232219352" Received: from binbinwu-mobl.ccr.corp.intel.com (HELO [10.124.240.207]) ([10.124.240.207]) by fmviesa009-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 14 May 2026 23:46:20 -0700 Message-ID: <90011488-83ba-4aa5-a753-28fa5fd4024d@linux.intel.com> Date: Fri, 15 May 2026 14:46:17 +0800 Precedence: bulk X-Mailing-List: linux-coco@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 02/15] KVM: x86/xen: Bug the VM if 32-bit KVM observes a 64-bit mode hypercall To: Sean Christopherson Cc: Paolo Bonzini , Vitaly Kuznetsov , Kiryl Shutsemau , David Woodhouse , Paul Durrant , Dave Hansen , Rick Edgecombe , kvm@vger.kernel.org, x86@kernel.org, linux-coco@lists.linux.dev, linux-kernel@vger.kernel.org, Yosry Ahmed , Kai Huang References: <20260514215355.1648463-1-seanjc@google.com> <20260514215355.1648463-3-seanjc@google.com> Content-Language: en-US From: Binbin Wu In-Reply-To: <20260514215355.1648463-3-seanjc@google.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 5/15/2026 5:53 AM, Sean Christopherson wrote: > Bug the VM if 32-bit KVM attempts to handle a 64-bit hypercall, primarily > so that a future change to set "input" in mode-specific code doesn't > trigger a false positive warn=>error: > > arch/x86/kvm/xen.c:1687:6: error: variable 'input' is used uninitialized > whenever 'if' condition is false [-Werror,-Wsometimes-uninitialized] > 1687 | if (!longmode) { > | ^~~~~~~~~ > arch/x86/kvm/xen.c:1708:31: note: uninitialized use occurs here > 1708 | trace_kvm_xen_hypercall(cpl, input, params[0], params[1], params[2], > | ^~~~~ > x86/kvm/xen.c:1687:2: note: remove the 'if' if its condition is always true > 1687 | if (!longmode) { > | ^~~~~~~~~~~~~~ > arch/x86/kvm/xen.c:1677:11: note: initialize the variable 'input' to silence this warning > 1677 | u64 input, params[6], r = -ENOSYS; > | ^ > 1 error generated. > > Note, params[] also has the same flaw, but -Wsometimes-uninitialized > doesn't seem to be enforced for arrays, presumably because it's difficult > to avoid false positives on specific entries. > > Signed-off-by: Sean Christopherson Reviewed-by: Binbin Wu > --- > arch/x86/kvm/xen.c | 7 +++++-- > 1 file changed, 5 insertions(+), 2 deletions(-) > > diff --git a/arch/x86/kvm/xen.c b/arch/x86/kvm/xen.c > index 91fd3673c09a..6d9be74bb673 100644 > --- a/arch/x86/kvm/xen.c > +++ b/arch/x86/kvm/xen.c > @@ -1694,16 +1694,19 @@ int kvm_xen_hypercall(struct kvm_vcpu *vcpu) > params[4] = (u32)kvm_rdi_read(vcpu); > params[5] = (u32)kvm_rbp_read(vcpu); > } > -#ifdef CONFIG_X86_64 > else { > +#ifdef CONFIG_X86_64 > params[0] = (u64)kvm_rdi_read(vcpu); > params[1] = (u64)kvm_rsi_read(vcpu); > params[2] = (u64)kvm_rdx_read(vcpu); > params[3] = (u64)kvm_r10_read(vcpu); > params[4] = (u64)kvm_r8_read(vcpu); > params[5] = (u64)kvm_r9_read(vcpu); > - } > +#else > + KVM_BUG_ON(1, vcpu->kvm); > + return -EIO; > #endif > + } > cpl = kvm_x86_call(get_cpl)(vcpu); > trace_kvm_xen_hypercall(cpl, input, params[0], params[1], params[2], > params[3], params[4], params[5]);